Application of Magnetostrictive Transducer for the Long-Range Guided Wave Inspection

Abstract:

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The leakage of the pipes is a major issue for the safety of industrial structures. However,
in many cases, because of their geometrical complexity and inaccessibility, it is difficult to inspect
them by the conventional NDE method. A long-range guided wave inspection, thus, is an option to
inspect them. A torsional vibration mode, T(0,1) shows many advantages in a long-range guided
wave examination of a pipe, such as no dispersion characteristic, no radial displacement and low
attenuation. However, it is not easy to fabricate a transducer with an array of piezoelectric elements
for generation of torsional vibration mode and even expensive. Recently a magnetostrictive metal
strip sensor was used for a generation of the torsional vibration modes in a pipe and this technique
has shown several advantages for practical applications. This study investigated the applicability of
a long-rang guided ultrasonic method to the detection of artificial notches even in the presence of
various foreign objects.

Abstract: Ultrasonic guided wave has been widely used for the pipe inspection. The conventional method is to use piezoelectric transducers that should be contacted to the target surface. However, in order to automatically inspect pipes in the manufacturing stage, non-contact inspections are strongly required. In this paper, we propose a new non-contact method for the automation of pipe inspection,
which generates the ultrasonic guided wave by laser and receives by air-coupled transducer. Also we have developed a rotational canning system to show the inspection result as a 2-D image, which makes the operator find out defects easily. Then, in practical applications of guided wave techniques, it is preferred to generate and detect a single or less dispersive mode. So this paper considers the
enhancement of mode-selectivity, where a laser beam illuminated through arrayed line slits is used as the transmitter and the air-coupled transducer is used as the receiver. The line arrayed laser illumination is a wavelength matching technique that can generate only a few modes. The air-coupled transducer detects the leaky wave of the propagated guided wave, and by tuning its detection angle we
can detect the selected single mode. This method can generate and receive the guided wave of a specific mode, which makes the interpretation of received signal clearer and resultantly improves the accuracy of inspection. The proposed method was applied to the stainless pipe specimen with artificial defects and its inspection performance was verified. The experimental results showed that the fundamental axial-longitudinal mode was dominantly generated and received, and the location
and the size of pipe defects could be displayed well in the 2 dimensional scanning images in real time.

Abstract: Conventional non-destructive techniques for inspection of weld in pipelines require
significant test time and high cost. In this paper, a study in the application of ultrasonic guided waves
to long range inspection of the pipeline is presented. The characteristics and setup of a long range
guided wave inspection system and experimental results in pipes of various diameters are introduced.
The experimental results in mock-up pipes with cluster type defects show that the limit of detectable
wall thickness reduction with this guided wave system is 2~3% in the pipe cross section area and the
wall thickness reduction of 5% in cross section area can be detected when actual detection level is
used. Therefore, the applicability of the ultrasonic guided wave technique to long range pipeline
inspection for wall thickness reduction is verified.

Abstract: Based on the theory of elastodynamics , the relationship between the amplitude of crack reversed echo and the size of crack which detection by the T(0,1) modal is studied by the method of simulation. Based on the simulation result, T(0,1) modal sensitive to a radial crack which length below the perimeter of pipe and the reflection ratio increase as the length of crack raised are got. The T(0,1) modal is insensitivity to a permeate axial crack which length between 20% to 45% of wavelength. The reflectance became minimum when the length arrive at 50% of wavelength, it get maximum when size reach 90% of wavelength, then it has a small decrease till 100%.

Abstract: The guided-wave technology is very efficient in inspecting a large portion of pipe. In order to study the propagation property of guided wave in pipe and the interaction between guided waves and defects, pipe model was established using 3D solid finite element in the software ANSYS. Tangential displacements were prescribed on the nodes in the pipe end and the propagating of T(0,1) mode guided wave in pipes was simulated. The detecting signals for the pipe model with different defects were extracted, which matched very well with experimental result.